The present invention relates to a method for tracking the location of mobile units.
There is currently a great need for the tracking of the location of mobile units, particularly wireless transmitters or transceivers that are worn or carried on a person, so as to keep track of that person""s location. The mobile units also can have sensors which sense voltage, temperature, vital signs, etc., and thus it is also important for the mobile unit to be able to transmit this information under adverse conditions.
Many problems arise from the use of such units, particularly where many units are present in a given area, and there is a need to accurately identify each individual unit, as well as to accurately identify the location of the unit.
The main object of the present invention is to provide a method for tracking the location of mobile units which is achieved by calculating the coordinates of the location of a mobile unit with a unique identification.
Another object of the present invention is to calculate the coordinates of the location of each mobile unit by measuring the phase difference of signals arriving at antenna elements of a phase array antenna at the base unit from a mobile unit.
Preferably, measuring of the phase difference is performed in the base unit, whereas the step of calculating the coordinates is performed in a main unit connected to the base unit and comprising a programmable computer, for example, an Intel Pentium II based personal computer having a Windows 98 operating system, or any kind of programmable computer system.
Each mobile unit may have one or more sensors, and the signal that is received from the mobile unit includes information or an information signal, may include an output from the sensor and a mobile unit address (identification number). The information from the sensor is processed preferably by the main unit.
The wireless transmitter or transceiver used in the mobile unit is preferably a radio frequency transmitter, and more preferably, a radio frequency transceiver.
Another object of the present invention is to improve the tracking method by a method for calibrating a system for tracking the location of mobile units.
Still another object of the present invention is to improve the accuracy of the location tracking by providing two or more base units disposed at a predetermined position apart from each other and measuring the azimuth of the signal received from each mobile unit at the antenna elements of the base units.
In accordance with the present invention, the base unit or phase difference measurement and communication unit (PDMCU) has the phase array antenna for receiving signals from a plurality of mobile wireless transmitter units or portable wireless interfaces (PWI) and at least one reference wireless transmitter or beacon is disposed at a fixed location. The beacon is at a known location with regard to the base unit and has a unique identifying address which identifies it as a beacon or reference unit.
A signal including the address is received from the beacon at the base unit via the phase array antenna. The phase difference between the signal arriving at the antenna elements from the beacon is measured and the coordinates of the location of the beacon are then calculated. Future calculations can then be corrected by the difference between the calculated coordinates of the beacon and the actual location of the beacon. Thus, when calculations are performed thereafter for mobile units, similar corrections can be performed to the calculated coordinates in order to find the actual location of those mobile units.
To further increase accuracy of the location detection, a plurality of base units can be used. In this case, the locations of the base units are known and each base unit will measure the azimuth direction of the mobile unit.
These and other objects and advantages of the present invention are achieved in accordance with the present invention disclosed in detail hereinafter with reference to the attached drawings, wherein